Geology mineral introduction to earth science

The orderly arrangement of atoms that make up the substance produce a definite and repeating geometric pattern = characteristic crystal form... Quarts or rocks and soils There are more

• What is a mineral?

• What is a gem?

• What is a rock?

• How are these formed?

• Edited from WARDS

Geometry of Crystals Lab

Mineral Criteria

1 occurs naturally on Earth

Mining: Dig for Diamonds Park

2 is inorganically formed ( does not contain

carbon) Exceptions are diamonds and

graphite = pure carbon

Criteria continued

3 a solid at standard temp and pressure

4 Elements that make up the substance are combined in fixed proportions

5 The orderly arrangement of atoms that

make up the substance produce a definite and repeating geometric pattern =

characteristic crystal form

Minerals

Is an element (ex Gold, Au)

or a compound (ex Quarts or

rocks and soils

There are more than 3500 minerals identified

New minerals are being

Mineral Identification

• Based on physical and chemical traits

• Initially classified using one or more of the following physical properties

• 1 color 5 specific gravity

• 2 luster 6 cleavage or

• 3 hardness fracture

• 4 streak 7 crystal form

• Least reliable trait

• Color can vary

• Color can change

when exposed to

moisture, high or low

temperatures or

weathering

• Physical appearance

of the unweathered surface

• Way it reflects sunlight

• Metallic or nonmetallic (glassy, pearly, silky, greasy or brilliant)

• Is the resistance of a mineral’s smooth surface (face) to being scratched by a

point or an edge

• Mohs Hardness Scale has a range

• 1 (soft, easily scratched – ex Talc) to

• 10 (hard – ex Diamond)

• Any mineral can scratch a mineral with a lower hardness

• Tools for Testing Hardness

• You typically do not carry around a

supply of the 10 minerals on the hardness scale However, you can use the following items to help estimate the hardness of a mineral:

• Finger Nail (H = 2.5)

• Penny (H = 3)

• Knife Blade (H = 5.5)

• http://zircon.mcli.dist.maricopa.edu/aaim/linear/L1.html

• Color of a mineral in its ground or powdered form

• The powder is formed when the mineral is

rubbed across an unglazed porcelain plate

• More reliable than color

• Plate has a hardness of 7 and is white

• Scratch test cannot be used on minerals of the same color or hardness

Specific Gravity (Relative Density)

• Specific gravity is the ratio of a mineral’s mass to the mass of an equal volume

water

• Very reliable

Cleavage or Fracture

Cleavage: a break along a smooth, flat plane producing smooth flat surfaces called faces

Ex Galena

Fracture: a break that is not smooth but produces irregular surfaces

Crystal Form

• One of the most useful physical

characteristics

• Crystal forms result from the internal

atomic arrangement of a mineral

• Repetition of these arrangements results

in crystal systems which produce the

visible shape of the mineral

Pyrite : “Fool’s Gold”

• FeS2

• Is the result of many atoms of iron and sulfur forming a crystalline solid with a definite internal arrangement

All crystals can be categorized into

1 of 6 crystal systems

• As defined by axes

• Axes are imaginary straight lines that pass through the center of the crystal faces at right angles to these faces and intersect

at the center of a perfect crystal

Isometric or Cubic

Characteristics

• 3 equal exes intersecting

at right angles to each

other

• Same measure

• 6 faces

• Each face is a square

• Angle between two

adjacent sides is 90 o

• Ex Galena, halite, pyrite

• Each of the similar 6

faces join each other at

60 o

• 2 more identical faces are

different form the other 6

• 2 identical faces form 90 o

with the other 6

• Ex Calcite, quartz and

apatite

• All adjacent faces hit

at 90 o

• Ex Chalcopyrite, zircon

• All adjacent sides meet at 90 o

• Ex Olivine, silfur, topaz

• 4 identical or similar faces

• 2 identical faces unlike

• 3 unequal axes

• None of the axes

intersect at 90 o

• Four similar or identical

polygons and 2 larger

• A gemstone or gem, also called a precious or

— when cut and polished — is used to make jewelry or other adornments [1] However certain rocks , (such as

are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well

Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties that have aesthetic value Rarity is another characteristic that lends value to a gemstone

Rocks (more info to come) 

Rocks are classified by mineral and chemical

composition, by the texture of the constituent

particles and by the processes that formed them These indicators separate rocks into igneous,

sedimentary and metamorphic They are further classified according to particle size The

transformation of one rock type to another is

described by the geological model called the

rock cycle.

• http://en.wikipedia.org/wiki/Rock_(geology)

Mining http://bldgblog.blogspot.com/2005/08/worlds-

largest-diamond-mine.html